Which of the following is NOT a type of chemical energy warhead?

The choice highlighting 'concussive' as an option that is not a type of chemical energy warhead is accurate because concussive effects primarily arise from the shockwave generated by an explosion rather than from chemical reactions. Concussive warheads focus on the physical impact of the explosion, delivering kinetic energy rather than utilizing a chemical energy reaction to cause destruction.

In contrast, direct contact, fragmentation, and incendiary warheads all rely on chemical reactions to function. Direct contact warheads often involve explosive materials designed to detonate upon impact, utilizing chemical energy for maximum effect. Fragmentation warheads are engineered to disperse shrapnel, which is typically produced through explosive chemical reactions designed to create lethal projectiles. Incendiary warheads use chemical compounds that ignite upon detonation, creating fires and causing damage through heat rather than solely through an explosive shockwave.

Thus, by focusing on the underlying principles, it's evident why 'concussive' does not belong to the same category as the other options, which are indeed types of chemical energy warheads.